Breakage rates of particles in a ball mill change with instantaneous particle size distribution in the mill. Slurry density and the presence of a grinding aid also affect breakage rates substantially. The effect of these variables, which constitute the mill environment, on breakage rates has been quantified with a unique estimation method known as the G-H method. This method enables the estimation of breakage rates of all size intervals by a simple linear graphical scheme. In general, breakage rates of coarse particles increase in the presence of fine particles, while the rates of fine particles remain relatively unaffected. Grinding aid restores the fluidity of the solid-liquid mixture even at very high percent solids and so the rate of grinding returns to ’normal’ from ’erratic’ behavior.